modification for chapter 6's persistenceContextCollision

[Himai Minh]

I modified this example:

//Change it from Stateful to Stateless
@Stateless
@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public class DepartmentManager {
    //change this PC from extended PC to transaction scoped PC
    @PersistenceContext(unitName="EmployeeService")
  
    EntityManager em;
    Department dept;
    @EJB AuditService audit;


     //Stateless , transaction scoped PC  of the department manager invokes 
    //Stateful extended PC of the audit bean, collision happens.
       public void addEmployee(int empId) {
        Employee emp = em.find(Employee.class, empId);
        dept.getEmployees().add(emp);
        emp.setDepartment(dept);
        audit.logTransaction(emp.getId(), 
                             "added to department " + dept.getName());
    }
    
    @TransactionAttribute(TransactionAttributeType.REQUIRED)
    public void addEmployee2(int empId) {
        Employee emp = em.find(Employee.class, empId);
        dept.getEmployees().add(emp);
        emp.setDepartment(dept);
        audit.logTransaction(emp.getId(), 
                          "added to department " + dept.getName());
         
    }

//Change it from stateless to stateful
@Stateful
public class AuditService {
    //Change it from transaction PC to extended PC.
    @PersistenceContext(unitName="EmployeeService",
    type=PersistenceContextType.EXTENDED)
    private EntityManager em;
    

Our expected result is collision:

javax.ejb.EJBException: There is an active transactional persistence context for the same EntityManagerFactory as the current stateful session bean's extended persistence context

[Himai Minh]

To make it work, let the stateful bean starts a new transaction instead of using the propagated transaction:

@Stateful
public class AuditService {
   
    @PersistenceContext(unitName="EmployeeService",
    type=PersistenceContextType.EXTENDED)
    private EntityManager em;
     @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
    public void logTransaction(int empId, String action) {
        // verify employee number is valid
        if (em.find(Employee.class, empId) == null) {
            throw new IllegalArgumentException("Unknown employee id");
        }
        LogRecord lr = new LogRecord(empId, action);
        em.persist(lr);
    }
    
  
}

Reference:http://shengwangi.blogspot.com/2015/11/understand-persistence-context-collision.html

[Himai Minh]

The reason why I suggested this modification because  the original code demonstrated another concept , not pc collision.
The original code tells us that an stateful bean  with container managed transaction  cannot run in a UserTransaction.
The output error message is actually:

javax.ejb.EJBException: java.lang.IllegalStateException: Bean is associated with a different unfinished transaction

Original code as Audit bean is stateless with transaction scoped PC and Department manager bean as stateful with extended PC.

@Stateless
public class AuditService {
   
    @PersistenceContext(unitName="EmployeeService")
    private EntityManager em;
   
    public void logTransaction(int empId, String action) {
        // verify employee number is valid
        if (em.find(Employee.class, empId) == null) {
            throw new IllegalArgumentException("Unknown employee id");
        }
        LogRecord lr = new LogRecord(empId, action);
        em.persist(lr);
    }
    
  
}

@Stateful
@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public class DepartmentManager {
    @PersistenceContext(unitName="EmployeeService",type= PersistenceContextType.EXTENDED)
   
    EntityManager em;
    Department dept;
    @EJB AuditService audit;

    public void init(int deptId) {
        dept = em.find(Department.class, deptId);
    }
    
    public Department getDepartment() {
        return dept;
    }
    
    @TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
    public String getName() {
        return dept.getName();
    }

    public void setName(String name) {
        dept.setName(name);
    }
    
    public void addEmployee(int empId) {
        Employee emp = em.find(Employee.class, empId);
        dept.getEmployees().add(emp);
        emp.setDepartment(dept);
        audit.logTransaction(emp.getId(), 
                             "added to department " + dept.getName());
    }
    
    @TransactionAttribute(TransactionAttributeType.REQUIRED)
    public void addEmployee2(int empId) {
        Employee emp = em.find(Employee.class, empId);
        dept.getEmployees().add(emp);
        emp.setDepartment(dept);
        audit.logTransaction(emp.getId(), 
                          "added to department " + dept.getName());
         
    }
    @Remove
    public void finished() {
    }
}

//In servlet code:

@Resource UserTransaction tx;
 .....
 try {
              // a container managed transaction cannot be run in a user transaction for a stateful bean.
                tx.begin();
                deptManager.addEmployee2(parseInt(request.getParameter("empId")));
                printManagementActions(out, deptManager);
                  tx.rollback();